To the Editor: Dr Ylinen and colleagues1 found that both strength (isometric) and endurance
(isotonic) training were superior to a control regimen of stretching and aerobic
exercise for relieving chronic neck pain. The authors also found that isometric
training improved strength more than did isotonic training.

I have 3 concerns about this study. First, isometric training is most
specifically designed to increase the isometric strength of particular muscles.2 Thus, use of isometric strength as an outcome measure
could result in significant bias in favor of the isometric group.